A new study suggests that whole grain diets may not be as beneficial as once believed to reduce two important risk factors for cardiovascular disease (CVD).

This finding casts doubt on the recommendations by the American Heart Association to eat whole grains in order to lower risks of heart disease, obesity and type 2 diabetes.

In this systematic analysis, a group of Cochrane-affiliated researchers reviewed nine randomised studies on the effect of a wholegrain diet, refined grain diet or a standard diet, on cholesterol levels and blood pressure.

Whole grains include most cereals, wheat, barley, rice, millet, maize and oats, while refined grains refer to things like wheat flour, enriched bread and white rice. A standard diet would include both.

The Cochrane review only looked at RCTs lasting from 12-16 weeks and left out those that did not report relevant outcomes or reported outcomes related to diabetes and measures of glucose and insulin or body weight alone.

No studies were included on the effect of whole grains on deaths from CVD or CVD events per se either.

After reviewing the evidence in the nine studies selected, researchers found no positive effects on blood cholesterol or blood pressure attributable to whole grain diets.